In a photoresist process of a semiconductor fabrication process, a liquid process is performed by supplying chemical liquid to the surface of a semiconductor wafer (hereinafter “wafer”). As a module for processing the liquid process, for example, a resist application module such as a resist application apparatus for supplying a resist to the wafer has been used, and a resist supply nozzle is provided therein to supply resist to the wafer. The resist supply nozzle is usually attached to a support body, and may be spaced from the support body or from a chemical liquid supply tube for a replacement when the resist supply nozzle is broken or overly contaminated.
However, after the resist is discharged from the resist supply nozzle, the residue of resist attached to the front-end of the nozzle and the inside wall of the inner flow path thereof may be dried and solidified. This may block a normal discharge of the resist in a subsequent wafer process. In an effort to prevent this problem, a suck back valve may be provided at the upstream side of the tube of the resist supply nozzle. The suck back valve is configured to suck the liquid of the flow path at the downstream side thereof toward the upstream side of the flow path.
The operation of resist supply nozzle 201 will be described when the suck back valve is provided at the tube. After the resist is discharged from resist supply nozzle 201 to the wafer, flow path 200 is sucked up by the suck back valve, thereby attracting remaining resist 202 at the front end and near the front end of flow path 200 toward the upstream side of flow path 200. Also, an air is introduced from the outside of resist supply nozzle 201 to the inside of the flow path to form an air layer 202 at the front end of flow path 200. Subsequently, from a thinner reservoir provided in the resist application module, the suck back valve sucks thinner 204 to the front end of flow path 200.
FIG. 23 illustrates the front end of resist supply nozzle 201 where thinner 204 is sucked up. It is noted that the drying process of resist 202 is suppressed by the blocking effect of flow path 200 by thinner 204. Air layer 203 takes a role to prevent resist 202 from being diluted due to mixing of thinner 204 and resist 202. When the resist application process is performed for the wafer from the state of FIG. 23, thinner 204 is first discharged outside the wafer to be drained out, and then the process is performed.
In this case, since thinner 204 sucked to the front end of resist supply nozzle 201 may be volatilized thereby causing resist 202 to be dried out, a so-called dummy dispense such as a resist discharge process that is not intended to process the wafer is jointly utilized. Also, the front end of resist supply nozzle 201 may be cleaned with the thinner to prevent the resist at the front end of resist supply nozzle 201 from being dried and solidified.
However, the amount of thinner and resist used in the process is increased by the blocking of the flow path of resist supply nozzle 201 with the thinner, dummy dispense and cleaning of resist supply nozzle 201 using the thinner. As a result, there is problem that the processing cost is increased. Also, there is concern that thinner 204 and resist 202 inside flow path 200 may drop onto the wafer by the shock applied to resist supply nozzle 201 while the resist supply nozzle is in motion, thereby causing a defect to the product.
Japanese Utility model Laid-Open No. Sho 62-58399 discloses a liquid transfer apparatus provided with a cutoff valve at the tube to block the supply of the liquid to the downstream side. However, since the distance from the cutoff valve to the nozzle at the downstream side of the tube becomes longer in the liquid transfer apparatus, the amount of the dried resist is increased, thereby increasing the amount of the liquid for the dummy dispense. Also, when a suck back operation is performed to prevent the drying of the liquid in the tube path of the liquid transfer apparatus as mentioned above, the sucking amount is increased because the liquid at the upper stream side than the cutoff valve needs to be sucked, thereby decreasing processing efficiency.
Also, Japanese Patent Laid-Open No. Hei 10-57850 discloses a resist supply apparatus equipped with a cutoff valve and a suck back valve at the upstream side tube of the nozzle. However, the resist supply apparatus in Japanese Patent Laid-Open No. Hei 10-57850 has similar problem to the liquid transfer apparatus of Japanese Utility model Laid-Open No. Sho 62-58399. Also, Japanese Utility model Laid-Open No. 53-92390 discloses a liquid supply apparatus equipped with a suck back valve and a cutoff valve at the upstream side tube of the nozzle. However, since these valves are provided at the tube, the same problem occurs as in the liquid transfer apparatus of Japanese Utility model Laid-Open No. Sho 62-58399. Furthermore, since the suck back valve is provided at the downstream side of the cutoff valve, it is impossible to prevent the drying of the chemical liquid sucked by the open/close operation of the cutoff valve.